Vascular anomalies (VAs), inborn errors in embryonic vascular development are classified into two distinct groups: hemangiomas and vascular malformations (VMs). Current therapies for VAs are limited in efficacy and have significant complications. Therefore, to improve therapy for patients afflicted with these conditions, it is critical to find new drugs or repurpose FDA-approved drugs to target VAs. Our long-term goal is to understand the underlying mechanisms that lead to pathogenesis of VAs so that better therapeutics targeting this condition can be generated. In order to pursue that goal, the objective is to identify small molecules (SMs) that will target dual-specific phosphatase-5 (Dusp-5), a member of the mitogen-activated protein kinase (MAPK) family, which is mutated in patients with hemangiomas and VMs. We have identified a serine to proline mutation at 147 AA in DUSP-5 (S147P), which results in a hypoactive phosphatase that is unable to dephosphorylate p-ERK. This results in sustained p-ERK levels, which is often associated with increased proliferation of cells such as those in VAs. Our central hypothesis is that, human S147P protein recapitulates zebrafish S148P protein function, whereby mutation perturbs the interaction with p-ERK such that DUSP5 phosphatase domain (PD) cannot be properly positioned to de-phosphorylate p-ERK. Small molecules such as SM1842, FDA-approved compounds (Suramin), and SM1842 analogs can reverse this effect, thereby permitting a switch between WT and S147P function both at the molecular level (in vitro), and in terms of cellular function. This hypothesis is formulated based on preliminary data from our group that predicts the incorrect positioning of the DUSP5 PD domain in relation to p-ERK using computational modeling studies on Dusp-5 interaction with ERK, which suggests the molecular mechanism that leads to the S147P<s hypoactivity. Further, computational docking approach with 10,500 SM compounds to the C-terminal PD of Dusp-5 enzyme identified SM1842, and other SMs that act as potent Dusp-5 antagonist in ECs. SM1842 is the most potent of the identified hits, acts as Dusp-5 antagonist in p-ERK assay, affects VEGF-stimulated p-ERK and Dusp-5 levels in endothelial cells, and restores S148P function in biochemical assays in vitro. Suramin - FDA-approved compounds (similar structure to SM1842) also affect endogenous Dusp-5 and p-ERK levels in endothelial cells. The proposed hypothesis will be tested by pursuing three specific aims: 1) Determine the structural mechanism for SM1842 in affecting Dusp-5 and S147P function; 2) Identify the optimal chemical analog for SM1842; and 3) Characterize the activity of FDA- approved compounds (suramin) similar to SM1842 in vivo and in vitro. In each of these aims, we will employ a variety of biophysical, cell biology, molecular and developmental biology approaches to unravel mechanistic basis for SM1842 and its analog to affect Dusp-5<s activity in vivo and in vitro. The approach is innovative because molecules like SM1842 that selectively affect mutant protein over WT protein, function are highly sought after by big Pharma, and this application has the potential to shift paradigm in target-based research. The proposed research is significant because benefits of this project will provide immediate clinical impact for VA patients in terms of therapy options, and importantly will translate basic science discovery into tangible clinical benefits instantaneously.